Water flows in the upward direction in a tank through $2.5\;m$ thick sand layer as shown in the figure. The void ratio and specific gravity of sand are $0.58$ and $2.7$, respectively. The sand is fully saturated. Unit weight of water is $10\:kN/m^3$.
The effective stress (in $kPa$, round off to two decimal places) at point $\textbf{A}$, located $1\:m$ above the base of tank, is ______.
